The fattest speaker at a recent conference on obesity was the anti-fat campaigner Kelly Brownell, who never tires of comparing Ronald McDonald to Joe Camel. If pointing to Brownell's gut or his extra chin seems mean, consider how you would feel about a chain-smoking anti-tobacco activist or a slots-playing anti-gambling crusader.

Brownell is not the only portly leader of the fight against obesity. John Banzhaf, the George Washington University law professor who is a conspicuous advocate of suing fast food companies, also could stand to lose more than a few pounds.

But according to Brownell, a psychologist who heads Yale's Center for Eating and Weight Disorders, their girth is not their fault. The problem is the "toxic food environment": Food is too cheap, too tasty, too readily available, and too heavily promoted. In such an environment, Brownell argues, people naturally expand, just like laboratory rats fed a cafeteria-style diet.

"It's very hard to blame (rising obesity) on personal irresponsibility," he asserted at the obesity conference, sponsored by the American Enterprise Institute. "Instead of taking an individual point of view . . . we need to think of why the nation is overweight."

But a nation does not get fat; individuals do, one sticky bun at a time. The nation cannot eat less and exercise more; only people can, and they will do so only if they're persuaded that the costs in terms of foregone pleasure and extra effort are worth it.

A collectivist mentality leads to collectivist solutions. "We have a real crisis," Brownell declared. "There's a public that needs to be protected, and some bold and decisive action is going to be necessary." Given such rhetoric, his proposals are remarkably lame: more bike paths, no soda in schools, special taxes on "junk" foods, restrictions on food advertising.

Meanwhile, Brownell rejects measures that would make a real difference. When I suggested (tongue in cheek, I hasten to add) that the government tax people for each pound over their ideal weight, he objected.

Brownell's complaint was not that such a system would be tyrannical because how much you weigh is your business, not the government's. Plainly, he doesn't believe that. Rather, he worried that a weight tax puts too much emphasis on individual responsibility rather than the environment.

So the prices people pay for food are part of the environment that encourages obesity, but the price they pay for being fat is not? It seems Brownell simply does not have the courage of his convictions.

Likewise, John Banzhaf told the Obesity Policy Report, "I don't think the government can order (people) to exercise." Why not? Which is more likely to make Americans thinner: suing McDonald's, or mandatory calisthenics in the public square every morning?

If you assume that slimming us down is a proper goal of government, it's hard to see the objection to policies that show promise of actually working, as opposed to enriching lawyers or making a statement. But perhaps there is something wrong with the assumption.

The main argument for government intervention in this area is that all of us pick up the tab for obesity-related disease when treatment is covered by taxpayer-funded health care programs. A recent study in the journal Health Affairs put the total medical cost at $93 billion a year, about half of it covered by Medicaid and Medicare.

But since overweight people tend to die earlier than slim people, they may not use as much health care in old age or draw on Social Security as much. Hence the net financial result could be a wash or, as in the case of smokers, taxpayer savings.

More important, the argument based on taxpayer-funded medical treatment proves too much. This rationale could be used to justify almost any interference in our personal lives, since nearly everything we do carries some risk of injury or disease. As University of Chicago law professor Richard Epstein pointed out at the AEI conference, the public policy problem is the subsidy, not the behavior.

One of Epstein's colleagues at the University of Chicago, economist Tomas Philipson, put weight trends in perspective by showing that Americans have been getting fatter for at least a century because of technological changes that have made food cheaper and work less strenuous. Those changes come with a cost, but on balance they have been tremendously beneficial. "We are better off being fatter and richer," Philipson said. "I would not want to go back."